The present disclosure relates to free radical polymerization processes employing chain transfer agents for controlling the molecular weight of polymer and copolymer product using a recoverable catalytic chain transfer agent. Removal of the catalyst at the end of the reaction results in colorless to lightly colored resins.
Techniques for controlling the molecular weight of polymer and copolymer with chain transfer agents are disclosed in the prior art, as described in U.S. Pat. Nos. 4,526,945 and 4,547,323, respectively. Problems associated with use of known chain transfer agents include undesirable odor, intense color, and broad molecular weight distribution in the resulting polymer. Improved chain transfer agents are of considerable interest to the chemical industry. Catalytic chain transfer (CCT) is a versatile technology that allows for effective molecular weight/chain length control in free radical polymerizations by controlling the amount of catalyst and initiator used. Materials with lower molecular weights (i.e., smaller chains) generally require the use of larger amounts of the catalyst system while those with higher molecular weights generally result from the use of lower catalyst concentrations.
Certain catalytic chain transfer agents such as various cobalt porphyrins, iron porphyrins, cobalt aza-porphyrins, cobalt hemiporphyrins, cobalt phthalocyanines, cobalt naphthapthalocyanines, cobalt dipyrrole bis(nitromethylidenes) and cobalt oxime complexes enable molecular weight control of free-radical polymerizations of methacrylates (such as methyl methacrylate), which can lead to the formation of small molecules (such as dimer, trimer, tetramer), oligomers or higher molecular weight poly(methacrylate) containing unsaturated end groups. The products from catalytic chain transfer can be used as macromonomers in further polymerization or copolymerization. Such macromonomers are commonly used in forming structured polymers particularly useful as dispersants, binders, and other additives in automotive exterior paints. Examples of such applications are described in U.S. Pat. Nos. 5,770,648; 6,635,690; and 5,955,532.
One limitation of CCT arises from the color of the homogeneous cobalt catalysts generally employed that cannot be easily removed from the product. U.S. Pat. Nos. 4,680,352, 4,694,054 and 4,886,861 disclose the use of cobalt(II) chelates in processes for free radical polymerization, wherein they act as catalytic chain transfer agents for controlling the molecular weight of the homopolymers and copolymers produced. The cobalt chelates are generally left in the polymer, or removed by extensive purification procedures, including filtering, ion exchange, chromatography, and the like. See, for example, U.S. Pat. Nos. 5,726,263 and 4,526,945. PCT Publication WO 87/03605 discloses the use of cobalt (III) compounds to produce oligomeric species by free radical polymerization of unsaturated monomers. These catalysts, while useful, are also not easily separated from the reaction mixture and typically remain in the final reaction product. Since colored catalyst species remain in the product, these versatile building blocks have limited use in applications that demand color-free and/or metal-free products such as clear coats used in automotive finishing and refinishing operations. Metal and color contaminant-free resins and catalysts that can be recovered and reused would have high value.
One aspect of the present disclosure is to provide novel catalysts for use as chain transfer catalysts in oligomerization and polymerization of olefinic monomers (preferably methacrylates and methacrylic acid derivatives), characterized in that said catalysts are homogeneous and display high activity during the polymerization stage of the process and can be easily removed after the polymerization reaction is completed by means of phase separation. Another aspect is to provide a process which uses these novel catalysts to yield macromonomer, oligomer, and polymer with less color than processes with conventional catalysts.